The major human blood group system, the histo-blood group ABO system, is defined by three carbohydrate determinants, the blood group A, B, and H epitopes. Glycans carrying the ABH determinants are found on glycoproteins, on glycolipids, or as free oligosaccharides. ABH antigens can be found on N- or O-linked glycans. The most common core structures described so far on O-linked glycans are core 1 (Galβ3GalNAc), core 2 (Galβ3(GlcNAcβ6)GalNAc), core 3 (GlcNAcβ3GalNAc), and core 4 (GlcNAcβ3(GlcNAcβ6)GalNAc). These have been shown to carry type 1 (Galβ3GlcNAc), type 2 (Galβ4GlcNAc), and type 3 (Galβ3GalNAca) structures Type 1 structures are mainly found as extensions of the core 3 and 4 structures, whereas type 2 chains (polylactosamine) are seen as extensions on the GlcNAcβ1,6 branch of core 2 structures.
Transplantation (Tx) across the ABO barrier is usually avoided in organ Tx because the risk of antibody-mediated rejection (AMR) due to preformed antibodies is often high This may also hold true in bone marrow transplantation, though it has long been the belief that blood group ABH incompatibility does not affect the outcome. However, in some cases it would still be desirable to transplant across the ABO barrier, one of the reasons being that it widens the pool of available donors for a particular recipient, even if it does not increase the total number of donors
Removal of anti-A or anti-B antibodies by extracorporeal immunoabsorption (EIA) or plasmapheresis (PP) has been shown to improve graft survival following ABO-incompatible organ Tx. Another method used for the prevention of AMR in both ABO-incompatible Tx and xeno-Tx is infusion of free oligosaccharides, but low affinity of antibodies for free saccharides and the short half-life of low-molecular-weight oligosaccharides in the circulation (Ye et al, 1994; Simon et al., 1998) prevents a wider use.